KR20070040304A - A process for tritium removal from water by transfer of tritium from water to an elemental hydrogen stream, followed by membrane diffusion tritium stripping and enrichment, and final tritium enrichment by thermal diffusion - Google Patents

Abstract

Transferring tritium from water based diffusion to basic hydrogens, followed by removal of tritium from water by membrane diffusion tritium stripping and concentration, and finally tritium concentration by thermal diffusion. The combination of treatment steps has the advantage of the large throughput acceptance of membrane diffusion at low tritium concentrations and the simplicity of the thermal diffusion with low throughput required for final concentration. The membrane diffusion step uses a microporous or hydrogen permeable metal membrane (Pd / Ag alloy), supported or unsupported. The diffusion method is compatible with any pretreatment for transferring tritium from tritized water to basic hydrogen. The treatment can be designed to operate at low pressures with a small gas inventory and there is no risk of excessive pressure.

Isotopes, membrane diffusion, thermal diffusion

Description

After transferring tritium from water to basic hydrogens, tritium is removed from the water by membrane diffusion tritium stripping and concentration, and finally tritium is concentrated by thermal diffusion {A Process for Tritium Removal from Water by Transfer of Tritium from Water to an Elemental Hydrogen Stream, followed by Membrane Diffusion Tritium Stripping and Enrichment, and Final Tritium Enrichment by Thermal Diffusion}

The drawings form a part of this specification, include exemplary aspects of the invention, and can be embodied in various forms. In some instances, it is to be understood that many aspects of the invention have been exaggerated or enlarged to aid in understanding the invention.

1 is a process flow diagram depicting a combined process in the present invention.

FIELD OF THE INVENTION The present invention relates generally to the field of regenerating tritium isotopes from water, and more particularly to the transfer of tritium from water to an elemental hydrogen stream, followed by membrane diffusion tritium stripping and concentration of tritium from water. The present invention relates to a method of removing and finally concentrating tritium by thermal diffusion. In order to extract tritium from the heavy water moderator system for nuclear reactors, several large plants have been set up in Canada, France and recently South Korea. Kalyanam and Sood "Fusion Technology" 1988, pp 525-528, compares the processing characteristics of these types of systems. Similarly, smaller hard water tritium regeneration systems have been designed for fusion applications (H. Yoshida, et al, "fusion Eng. And Design" 1998, pp 825-882; Busigin et al, "Fusion Technology", 1995 pp 1312- 1316; A. Busigin and SK Sod, "Fusion Technology" 1995 pp 544-549). All current large-scale systems use a pretreatment method that transfers tritium from water to basic hydrogen and then goes through a cryogenic distillation cascade process to separate most of the hydrogen isotopes.

Large-scale membrane (gas) diffusion systems are designed and built to separate uranium isotopes. M. Benedict, T. Pigford and H. Levi, "Muclear Chemical Engineering", McGraw Hill (1981), describe the gas diffusion technique as a whole. Gas diffusion has never been used for large scale hydrogen isotope separation.

As described in G. Vasaru et al, "The Thermal Diffusion Column", VEB Deutscher der Wissenschaften, Berlin, 1968, thermal diffusion columns have been used to separate small hydrogen isotopes since the 1950s. This technique has been limited in its use because it cannot be scaled up for greater throughput.

All current large-scale treatment methods for detritiation of water include (a) catalytic exchange reactions such as DTO + D ₂ ↔ D ₂ O + DT; (b) direct electrolysis of water, such as DTO → DT + ½O ₂ ; Or (c) water gas transfer reaction: based on the transfer of tritium from water to basic hydrogen, such as water decomposition by appropriate reactions such as DTO + CO → DT + CO 2 (Kalyanam and Sood "Fusion Technology" 1988, pp 525 -528; A. Busigin and P. Gierszewski, "Fusion Engineering and Design" 1998 pp 909-914; DK Murdoch et al, "Fusion Science and Technology" 2005, pp 3-10; KLSessions, "Fusion Science and Technology" 2005 , pp 91-96; J. Cristescu et al, "Fusion Science and Technology" 2005, pp 97-101; IR. Cristescu et al, "Fusion Science and Technology" 2005, pp 343-348).

Recently Pd / Ag membrane cascades have been proposed as an alternative technique for cryogenic distillation for application to ITER (D.L. Luo et al, "Fusion Science and Technology" 2005, pp 156-158). However, the hydrogen throughput of the proposed apparatus was 1000 times smaller than in the detrithiation system of CANDU reactor moderator water, such as the Darlington tritium removal plant. This alternative technique is suitable for small unit isotope separation, such as upgrading a plasma depleted gas containing about 50% deuterium and 50% tritium to a concentration of 90% tritium to be suitable for regeneration of fused fuel. High tritium throughput for large fusion devices renders small processing techniques, such as thermal diffusion, impractical. In general water detrithiation techniques for nuclear reactors, the tritium throughput is very small compared to ITER scale fusion machines, but the amount of water treated is very large.

The cryogenic distillation process for large-scale hydrogen isotope separation in the prior art has the following drawbacks:

1. the use of liquid cryogens with risks such as potential high pressures when warming or evaporating; Thermal stress due to very low temperature processing environment; The need for vacuum insulated cold box containers to contain cryogenic devices;

2. Many liquid hydrogen (and tritium) inventories that are almost confined to distillation column packings;

3. possibility of interruption of the processing line due to freezing of impurities;

4. complex and expensive processing equipment;

5. complex operation and maintenance cost;

6. non-modular processing that makes it difficult to maintain and upgrade spare equipment;

7. The need for batch operation desiccant and liquid nitrogen absorbent for refining feed to cryogenic distillation cascade.

Large-scale membrane diffusion has not been used to separate hydrogen isotopes in the past because of the fact that it is not commercially available and the concentration of tritium from 99 ppm to 99 +% purity requires multiple discrete compression steps. In competition with cryogenic distillation, the number of compression steps needs to be reduced, especially in tritium high concentration treatment results in which tritium material compatibility and stability are present.

Thermal diffusion has been successfully used for small-scale tritium separations, even up to 99 +% tritium, but the scale could not be easily scaled up for greater throughput. This is because the thermal diffusion column must be operated in a laminar flow mode, but on a large scale it must be operated in a disturbed flow mode (R. Clark Jones and WHFurry, "Reviews of Modern Physics", 1946, pp 151). -224). Alternative techniques for constructing a large number of thermal diffusion columns in parallel when the processing requirements are high are undesirable. Thermal diffusion columns also have low thermodynamic efficiencies, and insignificant at small scale may be problematic at large scale.

It is a primary object of the present invention to provide a large scale non-cryogenic diffusion based method for the detrithiation of hard and heavy water, which is simpler and more economical than conventional cryogenic distillation methods.

Another object of the present invention is to provide a method which is simpler to start, stop and operate than the conventional cryogenic distillation method.

Another object of the present invention is to provide a modular method which can be designed and upgraded more simply than the conventional cryogenic distillation process.

Another object of the present invention is to provide a method based on a standardization module that simplifies the maintenance and maintenance of the spare equipment.

It is another object of the present invention to provide a process with a basic hydrogen isotope inventory that is significantly smaller than the conventional cryogenic distillation process.

Another object of the present invention is to provide a method with a reduced risk for removing liquid cryogens compared to conventional cryogenic distillation methods.

Another object of the present invention is to provide a method for detrithiating water containing tritium in ppm and producing a product having a tritium concentration of 99% or more.

It is another object of the present invention to provide a continuous process that eliminates the need for batch operation, such as desiccants and liquid nitrogen absorbers typically used for disposition of cryogenic distillation systems.

Other objects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which one aspect of the invention is disclosed by way of illustration and illustration.

According to a preferred aspect of the present invention, a method is disclosed in which tritium is transferred from water to basic hydrogens, followed by removal of tritium from water by membrane diffusion tritium stripping and concentration, and finally concentration of tritium by thermal diffusion. The method combines one or more thermal diffusion columns for finally concentrating tritium to a membrane diffusion cascade for tritium stripping and primary concentration. Such bonding has the advantages of scale expansion of membrane diffusion at high throughput and low tritium concentration and simplicity of thermal diffusion at low throughput required for final concentration. This method involves Vapor Phase Catalytic Exchange (VPCE), Liquid Phase Catalytic Exchange (LPCE), Direct Electrolysis (DE), Combined Electrolysis and Catalytic Exchange (CECE), Water Gas Transfer Reactor (i.e. Palladium) Water decomposition by membrane reactor (PMR), or any pretreatment for transferring tritium from tritized water, including Hot Metal Bed Reactor (HMBR), to basic hydrogen. The treatment may be designed to operate at low pressures (approximately 1 atmosphere) at the high pressure side and thermally diffused portions of the membrane diffusion portion, but is not limited to such excesses as evaporation when the liquid cryogen is warmed in conventional cryogenic distillation. There is no risk of pressure.

Detailed description of the preferred embodiments is provided herein. However, the present invention can be embodied in various forms. Therefore, the specific details disclosed herein are not to be construed as limiting the invention, but rather as a representative basis for teaching those skilled in the art of using the invention in any suitable detailed system, structure or method and as a basis for a claim.

In accordance with the present invention, FIG. 1 shows a conceptual process flow diagram for a detrithiation system of water based on the present invention. The illustrated pre-system 10 is vapor phase catalytic exchange (VPCE) in which tritized water supply 11 flows to gas-liquid contactor 12 used to wet the detritized gas stream 13. Unevaporated water 14 remaining in gas-liquid contactor 12 may be recycled to feed 11 or returned to the source, depending on its application.

In this example, the temperature of feedwater 11 entering gas-liquid contactor 12 is adjusted to maintain the optimal hydrogen-water vapor ratio at the wetted gas top outlet 15, after which the tritium-rich water is exchange reaction DTO + D Passes the high temperature catalyst reactor 16 which reacts according to ₂ ↔ D ₂ O + DT.

However, this method is used to extract tritium from tritium-rich heavy or hard water according to any of the following reactions:

DTO + D ₂ ↔ D ₂ O + DT

HTO + H ₂ ↔ H ₂ O + HT

HTO + HD ↔ HDO + HT

Or more generally

QTO + Q ₂ ↔ Q ₂ O + QT

Q represents a hydrogen isotope H and D here. In all these reactions, the transfer of tritium from water to basic hydrogen takes place.

Significantly lower tritium concentrations in detrithiated water return stream 18 require a higher hydrogen to water vapor ratio in feed stream 15 to the catalytic reactor. However, in applications such as detrithiation of heavy water reactor moderator water, a low hydrogen to water vapor ratio is desirable to maximize the total tritium removal rate, since the primary purpose is to maximize the overall tritium removal rate.

Preposition system 10 shown in FIG. 1 is characterized by liquid phase catalytic exchange (LPCE), direct electrolysis (DE), combined electrolysis and catalytic exchange (CECE), and a water gas transfer reactor (ie, a palladium membrane reactor (PMR)). It may be replaced by other systems such as water cracking or hot metal bed reactors (HMBR). Similarly, gas-liquid contactor 12 may be another device such as a bicarbonate film, an evaporator, or the like.

Downstream of reactor 16, the water vapor condenses in condenser 17 and then returns to gravity detritized water 18. In the downstream portion of the condenser, the basic hydrogen isotope exits through the feed vacuum pump 19 as it penetrates through the Pd / Ag membrane 20 which can only permeate the basic hydrogen isotope. The Pd / Ag membrane 20 and the feed vacuum pump 19 may be one or more units that operate to achieve high regeneration rates of the hydrogen isotope. The non-permeable gas or vapor exits when it retentates through the pressure regulating valve 21 and is heated to a temperature sufficient to prevent condensation of the water vapor.

The outlet of the feed vacuum pump 19 is fed to the membrane diffusion cascade 22. Feed position 24 in the membrane diffusion cascade is shown in step 4. Since the feed position is a special application according to stripping needs, the feed position 24 in step 4 should only be regarded as exemplary. Each stage of the membrane diffusion cascade 22 consists of at least one compressor and one membrane. In order to increase the throughput, since the compressors are available in discrete sizes only, each stage can have several membranes and compressors connected in parallel. Stripping step 23 strips tritium to make detrithiated gas product stream 13 for recycling to pre-system 10. Concentration portion 25 concentrates tritium to a sufficient concentration to allow final concentration to be carried out by one or more (but practical) thermal diffusion column (s) 29. Tritium concentrate product 33 from membrane diffusion cascade 22 is fed to thermal diffusion column (s) 29 for final concentration.

Each membrane unit in the membrane diffusion cascade 22 has a high pressure retentate side 26, a low pressure permeate side 27 and a diffusion membrane 28. Diffusion membrane 28 is a microporous membrane whose aperture is generally smaller than the gas means free path or is a metallic membrane such as a Pd / Ag hydrogen permeable membrane. In both cases, the lighter isotope species diffuse through the membrane faster than the heavier species, resulting in heavier isotopes being concentrated on the retentate side of the membrane. The number of stripping and concentrating steps used in the system is determined by the number of steps needed to reduce the flow 33 to downstream thermal diffusion column (s) 29 and the system separation requirements to a practical value.

The membrane diffusion cascade 22 can be designed to operate at low pressures. In microporous membranes, the operating pressure cannot increase outside the point where the gas mean free path is substantially larger than the pore size.

There is no risk of high pressure present in the system design due to the presence of a limited gas inventory. This is very different from cryogenic distillation, which, when warmed, can cause excessive pressure when the liquid cryogen evaporates and explodes. In addition, the membrane diffusion cascade 22 has a small inventory, since it does not manipulate liquid hydrogen (liquid hydrogen has a molar density about three square times higher than a low pressure warm gas).

Depending on the application, one thermal diffusion column 31 is shown in FIG. 1, although several columns connected in parallel or in series may be practical. The heat spreading column consists of a cylindrical quenching rod 30 or hot-wire which is concentrated in a tube surrounded by a cooling jacket 32. Tritium product 36 exits from the bottom of column 31 and tritium depleted gas 34 returns to membrane diffusion cascade 22. Coolant 35 is generally water, but can in principle be a cooler material such as liquid nitrogen. The separation capability of the thermal diffusion column is improved when the ratio of hot to cold temperatures is large.

By combining the scale scalability of the high throughput membrane diffusion cascade 22 and the thermal diffusion columns 29 of one or more small throughputs, the combined treatment method is a practical step number of membrane diffusion cascade 22 and a practical number of Has a thermal diffusion column 29. Treatment choices may be undesirable on their own or impractical.

The combined membrane diffusion cascade 22 and thermal diffusion columns 29 are simpler to operate than conventional cryogenic distillation cascades. The order of start up, run, or stop is not complicated. The method is continuous without having to work in batches.

Although the invention has been described in connection with the preferred embodiments, it is not intended to limit the scope of the invention to particular forms, but alternatives and modifications that may be included within the scope and spirit of the invention as defined by the appended claims. It is intended to include, and equivalents.

The combined membrane diffusion cascade 22 and thermal diffusion columns 29 are simpler to operate than conventional cryogenic distillation cascades. The order of start up, run, or stop is not complicated. The method is continuous without having to work in batches.

Claims (3)

Transferring tritium from water to basic hydrogens, followed by removal of tritium from water by membrane diffusion tritium stripping and concentration, and finally tritium concentration by thermal diffusion. A method for separating hydrogen isotopes, in which large-scale membrane diffusion combines continuously with small-scale thermal diffusion for final concentration. Water by vapor phase catalytic exchange (VPCE), liquid phase catalytic exchange (LPCE), direct electrolysis (DE), combined electrolysis and catalytic exchange (CECE), water gas transfer reactors (ie, palladium membrane reactors (PMR)) Combined film diffusion and thermal diffusion methods compatible with decomposition, or any pretreatment for transferring tritium from tritized water to basic hydrogen, including a Hot Metal Bed Reactor (HMBR).

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